Process for the purification of copper



Patented Aug. 8, 1933 PATENT OFFICE PROCESS FOR THE PURIFICATION OFCOPPER George S. Evans, Bronxville, N. Y., asslgnor to The MathiesonAlkali Works, Inc., New York, 1 N. Y., a Corporation of Virginia NoDrawing.

Original application March 19,

1929, Serial No. 348,350. Divided and this application May 4 Claims.

This invention relates to improvements in the refining of copper inreverberatory furnaces in which copper is charged into the furnace andrefined therein. The present application is a division of my priorapplication, Serial No. 348,350, filed March 19, 1929, which issuedJanuary 12, 1932 as United States Letters Patent No. 1,841,020.

In one application of the present invention, there is charged into thereverberatory furnace, along with the copper charge to be melted, apredetermined amount of densely aggregated soda ash or of a refiningagent of which soda ash is the principal active constituent, and themelting operation is then carried out. The added soda ash melts beforethe copper charge melts and forms a low melting point slag or flux. Themolten soda ash, or the slag formed from the soda ash and impuritiesadmixed with the copper, forms a pool into and under which the moltencopper flows as it is melted, thus giving a protective covering over thebath of molten copper from the beginning of the melt. The molten sodaash also has the added advantage and effect of extending the period ofcontact with the molten copper, since it is present and exerts itsrefining action during the melting operation, thus prolonging the periodof refining by the soda ash slag without prolonging the duration of thewhole operation of melting and refining.

The addition of soda ash to the cold charge before melting thus hasvarious advantages, giving an improved refining of the copper during themelting operation, insuring that a thinlyfiuid slag will be produced,forming a protective layer over the molten copper, prolonging the periodof refining without prolonging the entire operation of melting andrefining, etc.

I have found that by adding a fiuxing material of a low melting point,such as fused soda ash, with the cold copper stock, this fiuxingmaterial will form a pool of slag of low melting point in the bottom ofthe furnace which serves to protect the molten copper from oxidation andfrom absorption of impurities such as sulfur from the fuel. This pool oflow melting point slag, which is formed before the melting ofthe copperbegins, also performs other useful services. In the case of fused sodaash, this begins to react with impurities contained in the charge wellahead of the period of complete fusion of the copper charge, forming afiuid active slag which exerts a refining action on the copper as itmelts and as the drops or streams of molten copper pass through the slagand remain in contact therewith, while the whole 11, 15231. Serial No.536,651

charge is being melted down. The refining action of the reagent is thusobtained during the melting-operation and this refining action isthusprolonged without prolonging the normal cycle of operations. In fact,this refining action of the 0 soda ash slag going on coincident with themelting operation has, in certain copper refining operations, materiallyreduced the total time of the refining cycle with a saving in fueloverhead, and increased output per furnace, etc. Furthermore, 5 thisaddition of soda ash to the cold charge results in bringing up the slagin the early stages of the melting period, thereby increasing thethermal efliciency of the furnace in certain other operations. Moreover,by bringing up the slag, it is possible to effect an earlier and cleanerfirst skim which removes impurities contained in the copper charged andwhich permits improved heating of the skimmed copper surfaces. Furtheradditions of soda ash can be made to improve the subsequent refiningoperation, particularly where the slag first formed isskimmed from thecopper during the early period of operation.

Copper is commonly charged into reverberatory furnaces in the form ofpigs or slabs and is there melted asa part of the copper refiningprocess. When fused soda ash is charged with the cold I copper, it ismelted ahead of the copper and reduces absorption of impurities such assulphur from the fuel and at the same time reduces arsenic and otherimpurities going in with the cold charge of copper, thus increasing thepurity of the bath of molten copper produced. For example, it has beenfound that arsenic-bearing blister copper which, when melted downwithout the addition of sodium carbonate, showed an arsenic content of0.06 but when melted down with the addition of sodium carbonate addedwith the cold charge gave a product containing only 0.02% arsenic.

This reaction of sodium carbonate which effects arsenic reduction ispromoted-by the presence of oxygen in the molten copper, and byoxidizing conditions, such as the maintenance of a slightly oxidizingfiame, or the addition of oxygen-bearing materials such as copper oxide,which may be added in the bottom of the furnace along with fused sodaash. In this instance the copper oxide is absorbed directly by themolten copper but other oxygen-bearing materials may be used.

The presence of oxygen in the copper bath also aids in the removal ofiron as iron oxides and the removal of sulfur by oxidation to sulfurdioxide gas. When remelting pure cathode copper, a reducing agent suchas carbon may be added with the soda ash to reduce the metal oxidizedduring the melting operation. When the reducing agent is properlyproportioned with sufficient soda ash to absorb sulfur and otherimpurities from the fuelsuch addition will greatly reduce the refiningcycle of operations. The refining action of the added soda ash is alsoaccomplished during the melting operation, although it may continueafter the copper is melted. It insures that the slag formed will be athinly fluid slag and that impurities charged into the furnace with thecopper which will combine with the soda ash will be so combined.

In certain operations, portions of the charge are added as cold stock,followed by additional copper charges added in the molten form. Here thesoda ash may be added with thecold stock in the furnace followed bysubsequent additions, added with the molten portion of the charge. Inthis operation, the soda ash (not necessarily densely aggregated) isadded to the molten copper in the container wherein it is conveyed to'the furnace, the soda ash fusing and flowing into the furnace with themolten copper. In some instances soda ash may be added only with thecold charge and in others onlywith the molten portion of the charge.Ordinarily the molten portion is added to the furnace shortly after thesolid charge is thoroughly heated up or almost melting. v 5

Where soda ash is added near the end of the refining operation, or wherethe slag present at the end of the melting or refining operationcontains a considerable excess of sodium carbonate, or is thinlyfiuidand highly basic, such slag is sometimes advantageously re-used. Itmay be left in the furnace and employed to fiux the first copper meltedwhen a new charge is introduced into the furnace, or the soda ashrefining slag may be skimmed off or otherwise removed from the" furnacefor re-use in the same or other furnaces where dense aggregated soda ashis required, thus giving a double advantage from the sodium carbonateadded, its action being first during the completion of the refining andmelting operation of the preceding charge and second during the initialstages of melting and refining of the following charge in the samefurnace or other refining operations.

In some cases the final soda ash refining is carried out in a chamberoutside of the furnace through which the molten copper passesafterleaving the furnace and this last refining slag being of relatively highpurity, is reclaimed for re-use in other refining operations.

In other operations the charge may be made up of molten copper entirely,and portions of it may be at different stages of refiLnement. The chargemay be added to the furnace all at once or in successive additions. Insuch operation the soda ash may be added to the whole charge outside thefurnace and thus conveyed to the furnace. Or, if the charge is added inseveral portions, the soda ash may be added wholly with the firstportion or some may be added with each addition of copper.

In certain other operations the refining operation is carried out instages. In applying the present invention to such processes the slagformed by the addition of soda ash to the copper before charging, or tothe bath in the furnace itself, in a later stage, may be recovered in afused form and used in an earlier stage.

By another method the molten copper fiowing from the furnace issubjected to a series of refining operations by which the molten copperis first treated with a partially spent refining agent and then withincreasing concentrations of refining agent and finally with the purerefining agent. The process may be so arranged that the refiningmaterial and the molten copper pass in counter-current to each other.The copper may pass through an elongated hearth through which therefining agent is passing in counter-current and in contact with themolten copper.

A refining action may also be carried out exteriorly to the furnace in areceptacle which may be unheated. Molten copper from the furnace isadded to the receptacle and refined copper is withdrawn in such a waythat a pool of molten copper is maintained in the receptacle. Analkaline slag is maintained inthe receptacle by adding such amounts of asoda ash refining agent as may be required.

Although the various modifications of the present invention justdescribed are described in connection with the use of soda ash only, itis to be understood and is intended that in any of these modificationscopper oxide or other similar oxygen-bearing material may be added ifdeemed desirable. I

i The fiuxing material is advantageously added in the form of fused sodaash briquettes, or pigs of about two pounds each, but may be added inmelted form with a portion of liquid charge. Where the soda ash is to beadded to a quiet pool of copper or a body of molten copper which is notbeing subjected to a hot blast, as in a ladle before or after therefining operation or in the furnace after the blast is removed, it maybe added in the regular powdered form and the resultant fused slag willconsist in large part of fused'soda ash and can be recovered and used asa densely aggregated soda ash in the furnace. In some operations, whenthe charge is added cold, the soda ash may be added in the powdered formin a suitable container with the cold charge. The amount of soda ashadded can be varied, depending upon the character of the copper charged,impurities contained in the copper, etc. Additional soda ash can beadded subsequently, after the charge is melted, and particularly wherethe slag first melted is skimmed off. The molten soda ash exerts itsrefining action upon the copper as well as its protective action, bothduring the melting of the copper, and during the subsequent maintenanceof the molten copper in the furnace prior to its use for casting orother purposes. It insures a thinly fluid slag, and a metal which can bemore readily cast; and which gives castings of superior properties.

While I have referred to the soda ash as exerting the refining action, Ido not desire to limit myself to the action of the sodium carbonate perse, since the action seems to be one in which the sodium carbonate isdecomposed into sodium oxide and carbon dioxide, with the sodium oxideactively taking part in the refining operation. The refining agent isadded, however, as sodium carbonate or. soda ash, and preferably in theform of cakes of fused soda ash, although other refining mediums canalso be employed, for example, mixtures of sodium carbonate and calciumcarbonate or lime or limestone, or calcium fluoride, which, when addedalong with the cold copper charge in the reverberatory furnace, willform a thinly fluid slag, with advantages such as those hereinbeforereferred to.

In my prior application, Serial No. 255,268, filed February 18, 1928,which issued May 20, 1930 as United States Patent No. 1,759,347, I havedescribed and claimed the operation of air furnaces for melting iron andsteel with addition of a soda ash refining agent to the metal bath. Thepresent application relates, in part, more particularly to the additionof a soda ash refining agent to the furnace along with the cold coppercharge and the carrying out of the melting operations so that the sodaash refining agent will be melted and will exert its protective andrefining action during the melting operation. The process of thisapplication can advantageously be carried out simultaneously with theprocess of said prior application, by continuing the action of the sodaash refining agent, for example, by adding further amounts of the sodaash refining agent during the subsequent operations, as described insaid prior application.

I claim:

1. The method of refining copper which comprises charging the copper, aflux material containing a refining agent of which sodium carbonate isthe chief active ingredient, and copper oxide into a reverberatoryfurnace and carrying out the melting and refining operation.

2. In the process of refining copper in a reverberatory furnace the stepof adding with the solid metal charge, a refining agent containingsodium carbonate as its chief active ingredient and an oxygen-bearingmaterial.

3. In the process of refining copper in a reverberatory furnace, the,step of adding with the solid metal charge, a refining agent containingsodium carbonate as its chief activev ingredient and copper oxide.

4. The method of refining copper in a reverberatory furnace to removeoxidizable impurities therefrom, which comprises supplying oxygen to themolten copper during the early portion of the refining treatment by theaddition of an effective solid oxygen-bearing and oxidizing material anda flux material containing a refining agent of which sodium carbonate isthe chief active ingredient.

GEORGE S. EVANS.

